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Topic Title: Changing CU's
Topic Summary: ESC advice
Created On: 26 April 2009 11:58 AM
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 26 April 2009 11:58 AM
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mark2spark

Posts: 1444
Joined: 15 November 2006

Opinions please.

Went to see a CU change job, small two up two down type of house, small 4 way board main sw no rcd rewireable fuses, PME, all earths ok, 1 x ring, 1 light circuit, 1 discontinued immersion circuit (now combi boiler), 1 x cooker circuit.
As it's my shout, I'd be comfortable with saying, due to the boxing in, that the cooker 6mm was deeper than 50mm from wall surface, so arguably dedicated and non rcd'able.

The problem is that a new main switch rcd CU will fit in the cupboard space just right, a doubled up rcd board won't fit at all, an RCBO'd board (still investigating the height bit) raises a possibility of too high to fit in space.

The ESC advice (at Q/A 7) states that more than one rcd should be used to minimise inconvenience when trips occur.

Well, to follow that through, it appears that you can't put a lighting circuit on the same rcd as a ring circuit then because there will always be a light circuit down, with associated inconvienience, in a trip situation, irrespective of how many lighting circuits there are in a dwelling.

So, i'd like to fit a rcd main sw 4 way board, and can't really see the problem with it.
Perhaps the red tape is obscuring my vision?

-------------------------
I am prone to talking complete bol***ks at times, please accept my apologies in advance.
 26 April 2009 12:13 PM
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DOUGIE1000

Posts: 4183
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i would try and go down the rcbo road instead of the 30mA main switch.

Height of Wylex is 230mm for all there NHRS boards

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 27 April 2009 12:57 PM
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OMS

Posts: 19861
Joined: 23 March 2004

Is it just me:

Went to see a CU change job


Why a consumer unit change then - if all the existing circuits appear fit for reconnection what is actually wrong with the existing con unit that warrants replacement and reconnection to an existing system

Regards

OMS

-------------------------
Failure is always an option
 27 April 2009 01:21 PM
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perspicacious

Posts: 7251
Joined: 18 April 2006

Don't you know anything OMS?

You can do a CU change in a morning and walk away not only with £500+ (cash) for less than £100 of materials but also leaving the client believing that it is a panacea and very happy that you didn't have to damage any decoration or lift any floorboards......

Regards

BOD
 27 April 2009 01:29 PM
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OMS

Posts: 19861
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Ahhh - I see BOD, and there was me thinking that there must be an engineering reason behind all this - instead it is driven by the filthy lucre - a sort of cheap rewire as it were.

And of course, if it's cash then I guess no paperwork either

Regards

OMS

-------------------------
Failure is always an option
 27 April 2009 01:34 PM
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spinlondon

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If it's a like for like change, does the Cu require an RCD at all?
To my mind, putting all of the circuits onto a single 30mA RCD would not comply with the Regs.

Edited: 27 April 2009 at 01:34 PM by spinlondon
 27 April 2009 01:34 PM
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perspicacious

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"And of course, if it's cash then I guess no paperwork either"

Well OMS, the installers whine about Part P but conveniently forget that had they complied with the Wiring Regulations for not only the installation but for the issuing of certificates with test schedules, Part P would never have been introduced......

Regards

BOD
 27 April 2009 01:39 PM
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sparkingchip

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fit a dual RCD unit with lots of spare ways for future use, put the lights on one RCD the Sockets on the other, then if the lights go off the table lamp, telly, etc will still work giving a little light about the house, i have in some cases put a new light next to the CU off the other RCD to the lighting one so they can see to reset the RCD/ MCB.

Andy
 27 April 2009 01:48 PM
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OMS

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To my mind, putting all of the circuits onto a single 30mA RCD would not comply with the Regs.


Of course it would - what regulation does it breach

fit a dual RCD unit with lots of spare ways for future use


But why - I still can't see what the DistBd is being changed anyway

Part P would never have been introduced......


Agreed, if the small concerns couldn't behave themselves then government would do it for them

Regards

OMS

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Failure is always an option
 27 April 2009 05:47 PM
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spinlondon

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The Regs now call for discrimination between circuits.
Having One RCD to cover the whole installation would mean that if there was a fault causing the operation of the RCD on a ring, the lights etc. would go off.
 27 April 2009 06:07 PM
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OMS

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True, but as the installation only has one lighting circuit anyway then (by your logic) it is already a breach of BS 7671 - we should be careful of not falling into this trap with RCD's when we don't apply the same logic to CPD's.

To be fair, the manufacturing sector has done such a marvellous job of hyping the multiple RCD issue that people are now beginning to belive the sales rhetoric

Regards

OMS

-------------------------
Failure is always an option

Edited: 27 April 2009 at 06:16 PM by OMS
 27 April 2009 06:08 PM
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perspicacious

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"The Regs now call for discrimination between circuits." spin

Could you enlighten us with the 16th Reg number which didn't require discrimation and the 17th Reg number that now does?

Regards

BOD
 27 April 2009 06:37 PM
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spinlondon

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Originally posted by: OMS
True, but as the installation only has one lighting circuit anyway then (by your logic) it is already a breach of BS 7671 - we should be careful of not falling into this trap with RCD's when we don't apply the same logic to CPD's.

To be fair, the manufacturing sector has done such a marvellous job of hyping the multiple RCD issue that people are now beginning to belive the sales rhetoric

Regards

OMS


Having one lighting circuit does not to my mind, or as far as I can see by my logic breach the regulations.
 27 April 2009 06:50 PM
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deapea

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Originally posted by: spinlondon
The Regs now call for discrimination between circuits.

Having One RCD to cover the whole installation would mean that if there was a fault causing the operation of the RCD on a ring, the lights etc. would go off.


How did a TT installation covered by a 100mA rcd ever comply?
 27 April 2009 07:00 PM
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spinlondon

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Never said that that a TT installation covered by a 100mA RCD didn't comply.
 27 April 2009 07:03 PM
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perspicacious

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"The Regs now call for discrimination between circuits." spin

Could you please enlighten us with the 16th Reg number which didn't require discrimation and the 17th Reg number that now does?

Regards

BOD
 27 April 2009 07:04 PM
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OMS

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Having one lighting circuit does not to my mind, or as far as I can see by my logic breach the regulations.


So why does my single front end RCD breach any regulations then.

We are either applying 314.1 relating to division of an installation in to circuits to minimise inconvenience, avod danger etc or we aren't.

technically, 314.1(iii) I would suggest that the single ligting circuit specifically breaches the regs rather than potentially does if controlled by a RCD that covers other circuits also - that's why I suggested that your logic was flawed

Regards

OMS

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Failure is always an option
 27 April 2009 07:11 PM
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spinlondon

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Dividing an installation into circuits is achieved by having a lighting, ring main, boiler and cooker circuit.
In a larger premises, one might want to separate the rings and lighting into up and down, or even loft, cellar, kitchen, cooker, freezer and outside lights.

Edited: 27 April 2009 at 07:12 PM by spinlondon
 27 April 2009 07:27 PM
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OMS

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Quite - thats why I disagree with this:

Having One RCD to cover the whole installation would mean that if there was a fault causing the operation of the RCD on a ring, the lights etc. would go off.


If you claim that a single RCD is not compliant I will argue that a single lighting circuit is also non complaint - go figure

Regards

OMS

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Failure is always an option
 27 April 2009 07:31 PM
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perspicacious

Posts: 7251
Joined: 18 April 2006

Come on OMS, let the poor guy answer my question about the Reg numbers before drawing and quartering him

Regards

BOD
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